1. Field of the Invention
The present disclosure generally relates to systems and methods related to detecting defects in reticles or photomasks. More particularly, the disclosure generally relates to systems and methods for detecting defects in reticles and/or the photomasks used to produce dies by comparing images (e.g., of said dies).
2. Description of the Relevant Art
Current demands for semiconductor devices with high density and performance associated with increased transistor and circuit speeds and improved reliability. Such demands require formation of semiconductor devices with greater precision and uniformity, requiring meticulous process monitoring.
One process used in the production of semiconductor devices is photolithography. In photolithography masks or “reticles”, are used to transfer circuitry patterns to semiconductor wafers. A photolithographic reticle includes an intricate set of geometric patterns corresponding to the circuit components to be integrated onto the wafer. Every reticle in a series is used to transfer its corresponding pattern onto a photosensitive layer. The transfer of the reticle pattern onto the photoresist layer is typically performed by an optical exposure tool, which directs light or other radiation through the reticle to expose the photoresist. The photoresist is used to form a photoresist mask, and the underlying polysilicon or metal layer is selectively etched in accordance with the mask to form features such as lines or gates.
It should be appreciated that any defect on the reticle, such as an extra or a missing chrome may transfer onto the fabricated wafer in a repeated manner. Thus, it is of importance to inspect the reticles and detect any defects thereupon.
Defects on a reticle or photomask are detrimental to wafer yield in the semiconductor manufacturing process. Traditionally, there have been two inspection modes, die-to-die (D:D) and die-to-database (D:DB). Both modes rely on one basic assumption: the number of defective pixels in a processing patch (defined as a small rectangular region on the photomask) is a small fraction of the total number of pixels present in the processing patch. Most of the algorithms take advantage of this assumption to reduce dynamic tool noises and photomask plate noises. For example, there have been methods to dynamically compensate for slight feature sizing differences between a test die and reference die. As a result, most of the defect detection methods are tailored to find defects on the order of 101 to 102 nm length scale.
However, these existing methods do not have the capability or sensitivity to detect defects that have length scales comparable to a processing patch. These so-called mesoscopic defects can be resulting from photomask writing errors. If un-detected, they can cause yield-limiting or yield-killing consequences.